1. Field of the Invention
The present invention relates to a polishing apparatus for polishing a workpiece such as a semiconductor wafer to a flat mirror finish, and more particularly to a polishing apparatus having a cleaning apparatus for cleaning a polished workpiece and/or a transporter such as a rotary transporter or a linear transporter for supplying workpieces.
2. Description of the Related Art
In semiconductor device manufacturing processes, semiconductor wafers are polished to a flat mirror finish in a semiconductor wafer fabrication process, and layers formed on semiconductor devices are polished to a flat mirror finish in a semiconductor device fabrication process. These polishing processes in the semiconductor wafer fabrication process and the semiconductor device fabrication process are performed by a polishing apparatus.
Conventionally, such a polishing apparatus has been designed as a dedicated polishing apparatus having a single function of polishing semiconductor wafers. The semiconductor wafers which have been polished by the polishing apparatus are transported to a next cleaning process by a movable container in which they are immersed in water to keep them from drying during transportation. However, the cleaning process tends to impair the cleanliness of a clean room, and the polished semiconductor wafers need to be transported by an operator or a manually operated transportation means. Further, a large installation space is required for two kinds of apparatuses comprising the polishing apparatus and a cleaning apparatus that is used to carry out the subsequent cleaning process.
In an effort to make the polishing process clean and reduce the installation space of the apparatus, there has been developed a polishing apparatus which performs both a polishing process and a cleaning process and which is of a dry-in and dry-out type for introducing semiconductor wafers therein in a dry condition and removing polished and cleaned semiconductor wafers therefrom in a dry condition.
On the other hand, the polishing apparatus having a single function of polishing semiconductor wafers has been improved to allow the cleanliness of a clean room to be maintained, and the polishing apparatus and the cleaning apparatus used in a cleaning process after polishing have an increased processing capability for thereby reducing the number of the polishing apparatuses used for polishing processes and the number of the cleaning apparatuses. As a result, the conventional dedicated polishing apparatus having a single function of polishing semiconductor wafers can reduce an installation space thereof to a degree which is equal to or smaller than the dry-in and dry-out type polishing apparatus.
However, in the dedicated polishing apparatus having a single function of polishing semiconductor wafers, the semiconductor wafers which have been polished by the polishing apparatus are transported still by an operator or a manually operated transportation means, as before. If the transportation means is automated, then it is difficult to handle the semiconductor wafers because the semiconductor wafers are stored in the movable water tank. Thus, the problems are presented by the transportation means in the conventional dedicated polishing apparatus.
Further, the dry-in and dry-out type polishing apparatus has a processing capability per unit time and unit installation area lower than the conventional dedicated polishing apparatus having a single function of polishing the semiconductor wafers. Thus, the number of apparatuses in the polishing processes is large, and a large installation space is required, and the running cost of the apparatuses is high.
The dry-in and dry-out type polishing apparatus has two cleaning apparatuses operable based on two different cleaning methods for cleaning semiconductor wafers which have been polished, in order to increase the processing capability per unit installation area. Such two cleaning apparatuses clean a semiconductor wafer in two stages, and are installed in a smaller installation area with minimum cleaning functions. However, as recent semiconductor devices have smaller circuit elements and finer interconnections in integrated patterns, there has been a demand for removing polished semiconductor wafers from the polishing apparatus in a higher level of cleanness, and therefore the cleaning stages for cleaning the polished semiconductor wafers have increased from two stages to three stages to meet such a demand. Specifically, such three cleaning stages include a process of removing fine particles attached to the polished semiconductor wafer, a process of removing metal ions attached to the polished semiconductor wafer, and a process of drying the clean polished semiconductor wafer. In some cases, two or more types of metal ions attached to the polished semiconductor wafer are removed by different chemicals supplied thereto, with the result that a total of four stages are involved in cleaning the polished semiconductor wafer. The four cleaning stages may be performed by respective four cleaning apparatuses, or two stages of the four cleaning stages may be performed by one of three cleaning apparatuses.
If three or more cleaning stages are carried out by two cleaning apparatuses, then two cleaning stages are performed by at least one cleaning apparatus, whose processing capability is thus reduced per unit time. If three or more cleaning apparatuses are provided in a row in a polishing apparatus, then the polishing apparatus becomes large in size, and has a reduced processing capability per unit time.